AST/HIR: Clarify what the optional name in extern crate items mean

src/libsyntax/ast.rs

@@ -2055,7 +2055,7 @@ pub struct Item {
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum ItemKind {
-    /// An `extern crate` item, with optional original crate name.
+    /// An `extern crate` item, with optional *original* crate name if the crate was renamed.
     ///
     /// E.g. `extern crate foo` or `extern crate foo_bar as foo`
     ExternCrate(Option<Name>),